1. Field of the Invention
The present invention relates to an amorphous-metal-coated structure in which, as a coating layer, an amorphous metal is formed on the surface of a base structure, and a method of producing same.
Since amorphous metal has a noncrystalline structure, it possess great mechanical strength and a small thermal expansion coefficient and is small in damage caused by radiation as well as being excellent in both chemical corrosion resistance and wear resistance. When employed for magnetic structure, amorphous metal further exhibits the following excellent properties: no structural defects in contrast to crystal structure having defect such as crystal grain boundaries; no crystal magnetic anisotropy; remarkably improved coercive force and specific magnetic permeability; and a high electrical resistivity. With the above-described various advantages, amorphous metal is known as "dream materials" and is expected to be applied to an extremely wide range of use, such as electromagnetic cores, various kinds of sensor, and electromagnetic clutches. An amorphous-metal-coated structure according to the present invention may be applied to various kinds of mechanical and electrical element, such as a magnetic member of, for example, a torque sensor, a magnetic head, a wear-resistant slide member, a corrosion-resistant filtering medium, and an electrode material for caustic soda electrolysis or a fuel cell.
2. Description of the Prior Art
As described above, amorphous metals have great mechanical strength and a small thermal expansion coefficient, and are excellent in both chemical corrosion resistance and wear resistance and therefore have been applied to various kinds of mechanical and electrical element. Further, amorphous metals have been used as magnetic materials for a variety of products by making use of their magnetic properties. For example, an amorphous metal has been used as a magnetostrictive material for a torque sensor (a sensor in which a magnetostrictive material is bonded to the surface of a drive shaft, and a change in magnetic characteristics of the magnetostrictive material which change is caused by the stress acting on the drive shaft is measured to thereby detect a degree of torque).
To bond an amorphous metal formed in a thin strip onto the surface of a drive shaft, methods employing an organic adhesive (an epoxy resin) or soldering have heretofore been used, such as that disclosed in the specification of Japanese Laid-Open Patent Publication No. 211030/1982 (U.S. Pat. No. 4,414,855, filed on June 1, 1981).
These methods, however, suffer the following problems. Since the joint between the drive shaft and the amorphous metal thin strip is unfavorably weak in its bonding strength, the amorphous metal thin strip is apt to separate from the drive shaft due to fatigue as a result of its use over a long period of time, or variation of the magnetic characteristics in response to applied stress is apt not to take place sufficiently.
Japanese Laid-Open Patent Publication No. 9034/1983 also discloses a torque sensor employing an amorphous metal thin strip as a magnetostrictive material which is bonded to the surface of a drive shaft. In the Publication No. 9034/1983, however, no practical method of bonding the amorphous metal thin strip is disclosed.
There is still another bonding method in which a magnetic material for a torque sensor is welded to a drive shaft by means of plating, such as that disclosed in the Japanese Laid-Open Patent Publication No. 101192/1973 (U.S. Pat. No. 3,861,206). By this method, however, it is not possible for the amorphous metal to be sufficiently firmly bonded to a base material.
Thus, in the above-described conventional bonding methods, it has been impossible for amorphous metals to exert their full beneficial properties.